Ukraine will push on with its military offensive against rebels in the east of the country until peace and order have been restored there, according to the country’s acting defence minister.

Speaking after 14 servicemen, including a general, were killed on Thursday when rebels shot down an army helicopter, Mykhilo Koval, said that Ukrainian forces would continue with military operations in border areas 'until these regions begin to live normally, until there is peace'.

He spoke after reports emerged claiming
Russia has withdrawn thousands of troops from the Ukraine border, just
hours after the helicopter attack.

A Ukrainian soldier controls a road on the outskirts of Izyum in the east. Ukraine's acting defense minister said troops had ousted separatists from parts of Donetsk

US Defence Secretary Chuck Hagel didn't provide any details following news of the withdrawal but described it as promising.

He
said: ‘They are not where they need to be and won't be until all of
their troops that they positioned along that border a couple of months
ago are gone.

‘We do know that thousands of Russian troops have been pulled back and are moving away.

‘But we also know that there are still thousands of Russian troops still there that have not yet moved.’

Separately, the Organisation
for Security and Cooperation in Europe (OSCE) said it had lost contact
with a five-member team in the east. Four members of another OSCE
mission are still being held by pro-Russian rebels after being detained
in Donetsk on Monday.

A Ukrainian soldier inspects an airborne combat vehicle at a checkpoint near Slovyansk on Friday

The
OSCE said in a statement published online that it lost contact with the
team, made up of four international workers and one Ukrainian
translator, in the Luhansk region late on Thursday.

An insurgent leader in the Donetsk region confirmed that members of the first group were in their custody. The rebels said that they would ‘deal with this and then release them’, but did not elaborate or give a specific timeframe.

Ukraine has waged an intensifying campaign against the pro-Moscow rebels, who have seized government and police buildings and want the region to join Russia.

President-elect Petro Poroshenko, who will be sworn in to office on June 7, has promised that the campaign against the rebels, who he compared to Somali pirates, would last ‘hours’ rather than months.

On Thursday, rebels shot down a helicopter carrying Ukrainian troops, killing soldiers and a general who was in charge of combat training.

David Cameron, the Prime Minister, has offered Mr Poroshenko continued support as the crisis in the divided nation continues to rage.

Memebers of the Ukrainian army inspect an area near Slovyansk on Friday after reports that separatists had been ousted from swathes of Donetsk

Mr Poroshenko will meet Mr Cameron face-to-face when international leaders gather in Normandy next week for D-Day commemorations.

A spokesman for Mr Cameron: ‘praised the Ukrainian people for their determination to hold elections in such difficult circumstances and choose their own future.

‘The two leaders discussed how Mr Poroshenko would deal with the separatists in the east of Ukraine.

‘They agreed that a strong message must continue to be sent to Russia to cooperate in helping to end the ongoing violence - especially in securing the border to stop the movement of weapons.

‘The PM praised Mr Poroshenko's clear messages on democracy and financial and political reform and offered his continued support in helping him to build a secure and prosperous Ukraine through an inclusive national dialogue.’